SC 554: Appeared in 1942 as new proposed primary routing running from US 21 (now SC 72-121) and SC 901 around the east side of Rock Hill to end at US 21 (now SC 322) northeast of Rock Hill.
In 1948, SC 554 was renumbered as US 21 ALT (now SC 121 and the US 21 Bypass).

SC 554 around Rock Hill
1942 Official

US 21 ALT shown explicitly as the bypass designation
1948 City of Rock Hill